Abstract:

In a wireless communications system, such as a multiband Ultra Wideband
communications system, data is tranmitted by means of the phases of
pulses in multiple frequency bands. Data is encoded in the phase
difference between a pulse and a previously transmitted pulse. The
previously transmitted pulse may be the immediately preceding pulse in
the same frequency band, or may be separated from the present pulse by a
number of intervening pulses.

Claims:

1. A communications system, in which data is transmitted by means of
pulses in multiple frequency bands, wherein data is encoded in the phase
of a pulse in a frequency band relative to the phase of a previously
transmitted pulse.

2. A communications system as claimed in claim 1, wherein data is encoded
in the phase of a pulse in a first frequency band relative to the phase
of a previously transmitted pulse in said first frequency band.

3. A communications system as claimed in claim 2, wherein data is encoded
in the phases of pulses in each of said frequency bands, relative to the
phases of previously transmitted pulses in said respective frequency
bands.

4. A communications system as claimed in claim 2, wherein data is encoded
in the phase of a pulse in a first frequency band relative to the phase
of an immediately preceding pulse in said first frequency band.

5. A communications system as claimed in claim 2, wherein data is encoded
in the phase of a first pulse in a first frequency band relative to the
phase of a second pulse in said first frequency band, said second pulse
being separated from said first pulse by a plurality of intervening
pulses.

6. A communications system as claimed in claim 1, wherein data is encoded
by means of a binary coding scheme, such that a pulse having a first
phase difference Φ1 from the previously transmitted pulse
represents a binary `1`, while a pulse having a second phase difference
Φ2 from the previously transmitted pulse represents a binary `0.

7. A communications system as claimed in claim 1, wherein data is encoded
by means of a multi-phase coding scheme, defining a plurality N of
possible phase differences Φk=kπ/N, where k=0, 1, . . . ,
N-1, between the phase of a transmitted pulse and the phase of the
previously transmitted pulse, with each of the possible phase differences
encoding a different multi-bit binary value.

8. A communications system as claimed in claim 1, wherein the
communications system is an Ultra Wideband wireless communications
system.

9. A method of transmitting data in a multiband wireless communications
system, the method comprising: encoding data in the phase of a pulse in a
frequency band relative to the phase of a previously transmitted pulse.

10. A method as claimed in claim 9, wherein data is encoded in the phase
of a pulse in a first frequency band relative to the phase of a
previously transmitted pulse in said first frequency band.

11. A method as claimed in claim 10, wherein data is encoded in the phases
of pulses in each of said frequency bands, relative to the phases of
previously transmitted pulses in said respective frequency bands.

12. A method as claimed in claim 10, wherein data is encoded in the phase
of a pulse in a first frequency band relative to the phase of an
immediately preceding pulse in said first frequency band.

13. A method as claimed in claim 10, wherein data is encoded in the phase
of a first pulse in a first frequency band relative to the phase of a
second pulse in said first frequency band, said second pulse being
separated from said first pulse by a plurality of intervening pulses.

14. A method as claimed in claim 9, wherein data is encoded by means of a
binary coding scheme, such that a pulse having a first phase difference
Φ1 from the previously transmitted pulse represents a binary
`1`, while a pulse having a second phase difference Φ2 from the
previously transmitted pulse represents a binary `0.

15. A method as claimed in claim 9, wherein data is encoded by means of a
multi-phase coding scheme, defining a plurality N of possible phase
differences Φk=kπ/N, where k=0, 1, . . . , N-1, between the
phase of a transmitted pulse and the phase of the previously transmitted
pulse, with each of the possible phase differences encoding a different
multi-bit binary value.

16. A method as claimed in claim 1, wherein the communications system is
an Ultra Wideband wireless communications system.

17. A method of receiving transmitted data, the method
comprising:determining the phases of pulses received in at least one
frequency band, relative to the phases of pulses previously received in
said frequency band; anddecoding transmitted data on the basis of the
relative phases.

18. A method as claimed in claim 17, wherein the communications system is
an Ultra Wideband wireless communications system.

19. A transmitter, for use in a multiband wireless communications system,
the transmitter comprising:frequency generators, for generating signals
at a plurality of frequencies in respective frequency bands;a plurality
of modulators, for generating modulated pulses at said plurality of
frequencies;wherein said plurality of modulators are adapted to generate
modulated pulses, such that the phase of a pulse at a first of said
plurality of frequencies, relative to the phase of a previously
transmitted pulse at said first frequency, is determined by data to be
transmitted.

20. A transmitter as claimed in claim 19, wherein said frequency
generators comprise a single local oscillator reference frequency
generator, and means for generating said signals at said plurality of
frequencies in respective frequency bands there from.

21. A receiver, for use in a multiband wireless communications system, the
receiver comprising:frequency generators, for generating signals at a
plurality of frequencies in respective frequency bands;means for
detecting phases of pulses transmitted at said plurality of frequencies,
wherein said means for detecting phases is adapted to determine phase
differences, between the phases of pulses at a first of said plurality of
frequencies, relative to the phases of respective previously transmitted
pulses at said first frequency; andmeans for decoding transmitted data
from said determined phase differences.

22. A receiver as claimed in claim 21, wherein said frequency generators
comprise a single local oscillator reference frequency generator, and
means for generating said signals at said plurality of frequencies in
respective frequency bands there from.

Description:

[0001]This invention relates to wireless communications, and in particular
to a method for encoding data in a wireless communications system. More
particularly, the invention relates to a system and a method for encoding
data, for use in an Ultra Wideband (UWB) wireless communications system.

[0002]The term Ultra Wideband is used to refer to a number of different
wireless communications systems. In one form of Ultra Wideband (UWB)
communications system, a transmitter encodes data to generate a series of
pulses, which are transmitted at radio frequencies. The function of the
receiver is then to detect these pulses, in order to be able to extract
the data from the transmitted signal.

[0003]In one particular proposed form of UWB communications system, the
available bandwidth is divided into multiple bands, and data symbols are
divided into multiple pulses, with the pulses making up a symbol being
transmitted in different bands. The data is transmitted by encoding the
data onto the phase, or polarity, of a carrier signal within each of the
multiple bands. Thus, within each of the frequency bands, a pulse
transmitted with a first phase, or polarity, represents a first binary
value, while a pulse transmitted with a second phase, or polarity,
represents a second binary value.

[0005]Within the receiver in such a system, therefore, it is necessary to
detect the phase of the received pulses, within each of the frequency
bands, in order to be able to determine the data which is being
transmitted in that band. One problem which arises with this is that it
is necessary to have extremely stable, and identical, reference frequency
generators in the transmitter and the receiver. In practice, it is
extremely difficult to achieve this, however.

[0006]According to a first aspect of the present invention, there is
provided a communications system, in which data is transmitted by means
of the phase of a pulse transmitted in one of said frequency bands,
relative to the phase of a previous pulse signal transmitted in said one
of said frequency bands.

[0007]The fact that data is encoded in the relative phase of two pulses
means that it is not necessary to be able to measure the absolute phase
of each pulse with high accuracy.

[0008]Also, although it may be advantageous, it is not essential for the
local oscillators, which generate the signals at the frequencies of said
frequency bands, to be coupled together.

[0009]According to a second aspect of the invention, there is provided a
method of transmitting and receiving data in a multiband wireless
communications system, the method comprising: in at least one frequency
band, transmitting a series of pulses, such that the phases of said
pulses relative to predetermined previously transmitted pulses encodes
transmitted data; and, in a receiver, determining the phases of said
pulses relative to the phases of the previously transmitted pulses, and
decoding the transmitted data.

[0010]The method may advantageously be applied in each frequency band of a
multiband wireless communications system, for example an Ultra Wideband
(UWB) wireless communications system.

[0011]FIG. 1 is a block schematic diagram of a transmitter forming part of
a radio communications system in accordance with the invention.

[0012]FIG. 2 is a block schematic diagram of a receiver in a system in
accordance with the present invention.

[0013]FIG. 3 is a flow chart illustrating a method of operation of the
system in accordance with the invention.

[0014]FIG. 1 is a block schematic diagram of a transmitter 100, forming
part of a wireless communications system. In particular, the invention is
described herein with particular reference to its application in a
multiband Ultra Wideband (UWB) wireless communications system. A
definition of UWB systems is that a signal occupies a bandwidth of more
than 500 MHz, in the band from 3.1 to 10.6 GHz. In one type of UWB
system, the available bandwidth is divided into multiple individual
bands. In this illustrated embodiment of the invention, there are nine
such bands, although the exact number can be different in different
implementations of the invention.

[0015]In the transmitter illustrated in FIG. 1, the data which is to be
transmitted is generated and/or processed in a digital signal processor
(DSP) 102 of the transmitter 100. The data is then passed to a timing
generator 104, where it is divided amongst the nine separate frequency
bands. As illustrated in FIG. 1, the transmission path 106 for the first
band includes a pulse shaper 108, in which a pulse, or burst, is formed
from the data being transmitted from the first transmission path 106. The
first transmission path 106 further includes a first transmitter local
oscillator (TLO1) 110, which generates a frequency in a first band of the
total available bandwidth.

[0016]The pulse from the pulse shaper 108, and the first local oscillator
signal from the local oscillator 110, are then supplied to a gate 112, in
which the pulse, or burst, is used to modulate the local oscillator
signal.

[0017]The other transmission paths operate in the same way, although in
FIG. 1 only the ninth transmission path 116 is shown, for simplicity.
Thus, the data allocated for transmission in the ninth frequency band is
passed to a pulse shaper 118, and the resulting pulse is combined with a
local oscillator signal from a ninth transmitter local oscillator (TLO9)
120 in a gate 122, to form a signal at a frequency in the ninth band.

[0018]In principle, the phases and frequencies of the local oscillators
TLO1-TLO9 can be independent, and can be generated separately. However,
in practice, it is advantageous for the phases and frequencies of the
local oscillators to be at least somewhat related. For example, in one
preferred embodiment of the invention, the local oscillator frequencies
TLO1-TLO9 may all be obtained from just one standard local oscillator,
with phase locked loops establishing the desired relationship between the
local oscillator signals, although this is not essential.

[0019]Further, in accordance with the present invention, the phases of the
pulses generated by the pulse shapers 108, 118 are used to encode the
data which is to be transmitted.

[0020]More specifically, in this illustrated embodiment of the invention,
in each of the frequency bands, the data is encoded in the phase
difference between the phase of a transmitted pulse and the phase of a
previously transmitted pulse.

[0021]Still more specifically, in this illustrated embodiment of the
invention, in each of the frequency bands, the data is encoded in the
phase difference between the phase of a transmitted pulse and the phase
of the immediately preceding pulse.

[0022]For example, in the case of a binary coding scheme, a pulse having a
first phase difference Φ1 from the immediately preceding pulse
may represent a binary `1`, while a pulse having a second phase
difference Φ2 from the immediately preceding pulse may represent
a binary `0.

[0023]Other, more complex, multi-phase coding schemes are also possible.
For example, a coding scheme can define any number N of possible phase
differences Φk, for example kπ/N, where k=0, 1, . . . , N-1,
between the phase of a transmitted pulse and the phase of the immediately
preceding pulse, with each of these phase differences encoding a
different multi-bit binary value.

[0024]It will be noted that only phase differences Φ between 0°
and 180° are chosen, such that no ambiguity arises between phase
differences +Φ and -Φ.

[0025]Although the invention is described in this embodiment such that it
is the phase difference between two successive pulses which encodes the
transmitted data, it would also be possible to encode transmitted data in
the phase difference between a pulse and any previously transmitted
pulse. For example, in a sequence of pulses pi, for i=0, 1, 2, 3, .
. . , the transmitted data can be encoded in the phase difference between
pulses pi and p.sub.(i-4). That is, the transmitted data is encoded
in the phase difference between two pulses separated by three intervening
pulses. This allows four interlaced streams of pulses to be transmitted
in a frequency band. It will be realized that the transmitted data can be
encoded in the phase difference between two pulses separated by any
number of intervening pulses. However, this number should not be selected
to be too large.

[0026]An advantage of the present invention is that it is not necessary
for the absolute value of the phase of the transmitted pulses to be
known, provided that the uncertainty remains sufficiently constant
between the two pulses whose phase difference encodes the transmitted
data. Where the transmitted data is encoded in the phase difference
between two pulses separated by a number of intervening pulses, this
places a greater requirement on the stability of the transmitter and the
receiver.

[0027]The signals generated by the gates in the nine transmission paths
are then combined in an adder 124, and the resulting signal is amplified
in a power amplifier 126, before being passed to a transmit antenna 128.

[0028]FIG. 2 is a block schematic diagram showing the form of a receiver
200, adapted to receive signals transmitted from a transmitter 100 of the
type shown in FIG. 1.

[0029]Signals are received at an antenna 202, and then amplified in an
amplifier 204. The resulting signal, containing components in all of the
frequency bands, is then passed into nine reception paths, each of which
detects the signals in a respective one of those frequency bands.

[0030]Thus, in a first reception path 206, a first receiver local
oscillator (RLO1) 208 generates a local oscillator signal at a frequency
within the first band, and this local oscillator signal is passed to a
first mixer 210, and is passed through a 90° phase shifter 212 to
a second mixer 214. The mixers 210, 214 are connected to receive the
received signal passed into the first reception path 206, and therefore
detect the in-phase and quadrature components of that signal at the first
local oscillator frequency. The in-phase and quadrature components are
both detected, to avoid the possibility that the phase of the received
signal is at 90° to the phase of the local oscillator signal, in
which case the received signal may not be detected.

[0031]The outputs of the mixers 210, 214 are passed to respective
integrators 216, 218, and the integrated outputs are passed to respective
blocks 220, 222, which each perform a sample and hold function and an
analog-digital conversion function. As a result of the high data rate
which can be achieved in a UWB communications system, these blocks need
to sample the signal at an appropriately high rate. For example, the
sample period may need to be of the order of 100 ps-1 ns.

[0032]The blocks 220, 222 therefore produce respective digital outputs
representing the in-phase and quadrature components of the signal at the
first local oscillator frequency. These signals are then passed to a
digital signal processor 224. Together, the digital outputs representing
the in-phase and quadrature components of the signal at the first local
oscillator frequency are a suitable measure of the signal received at
that frequency.

[0033]Again, the receiver 200 contains nine such reception paths, of which
only the first and the ninth are shown in FIG. 2 for the purposes of
simplicity.

[0034]In the ninth reception path 226, the ninth receiver local oscillator
(RLO9) 228 generates a local oscillator signal at a frequency in the
ninth frequency band, and this is passed to a corresponding first mixer
230, and through a 90° phase shifter 232 to a corresponding second
mixer 234. As before, the outputs of the first and second mixers 230, 234
are passed to respective integrators 236, 238, and then to blocks 240,
242 which perform sample and hold and analog-digital conversion
functions.

[0035]As in the first reception path 206, therefore, the blocks 240, 242
generate digital signals representing the in-phase and quadrature
components of the signal in the ninth frequency band. Again, these
digital signals are passed to the digital signal processor 224.

[0036]In order to ensure that the received signals are detected correctly,
it is necessary that the local oscillators RLO1-RLO9 in the receiver have
frequencies, and phases, which are sufficiently close to the frequencies
and phases of the local oscillators TLO1-TLO9 in the transmitter 100.
Thus, as discussed above with reference to the generation of the local
oscillator frequencies TLO1-TLO9 in the transmitter, steps must also be
taken to ensure that the local oscillator frequencies RLO1-RLO9 meet
these required conditions. As in the transmitter, for example, the local
oscillator frequencies RLO1-RLO9 may all be obtained from just one
standard local oscillator. In this case, phase locked loops can then be
used to establish the desired relationship between the local oscillator
signals.

[0037]In accordance with this embodiment of the present invention, the
detected information depends on the differences of the phases of the
pulses received in each frequency band, and so the absolute values of the
phases are less important.

[0038]FIG. 3 is a flow chart illustrating a presently preferred method of
detecting the transmitted data in the receiver 200.

[0039]In step 301 of the process, received signals are detected in the
frequency bands of the system. In the description below, only a first
frequency band will be considered further, although the same process is
carried out for each frequency band, either dependent on the other
frequency bands, or independently of the other frequency bands.

[0040]In step 302, the phase of the received pulse in the first frequency
band are detected. As mentioned above, the blocks 220, 222, 240, 242
generate digital signals representing the in-phase and quadrature
components of the signals in the respective frequency bands. These can
then be used in the digital signal processing block 224 to detect the
phase angles of the respective signals.

[0041]In step 303, the detected phase angle of the received pulse in the
first frequency band is compared to the phase angle of a previously
received pulse. As described above, the previously received pulse of
interest may be the immediately preceding pulse, or may be a pulse
separated from the present pulse by a known number of intervening pulses.

[0042]As described above, the transmitter uses these phase differences to
encode data for transmission, and so the receiver can detect the
transmitted data from the detected phase differences.

[0043]Thus, depending upon the coding scheme used in the transmitter, as
described above, the determined phase difference represents a particular
binary value, which may be a multi-bit binary value.

[0044]Thus, in step 304, the receiver detects the binary value,
represented by the detected phase difference, for the received pulse.

[0045]This procedure is carried out for each received pulse in each of the
nine frequency bands, either dependent on the other frequency bands, or
independently of the other frequency bands, and the transmitted data can
be recreated.

[0046]Thus, the system and method described herein allow the accurate
detection of the transmitted data. Further, the arrangement has the
advantage that the requirements imposed on the frequency generation are
greatly reduced. That is, any moderate variation in the local oscillators
within the transmitter or will not affect the detection of the data in
the receiver. Similarly, there is a reduced requirement for absolute
frequency accuracy in the local oscillators within the receiver.

[0047]In summery the invention relates to a wireless communications
system, such as a multiband Ultra Wideband communications system, in
which data is transmitted by means of the phases of pulses in multiple
frequency bands. Data is encoded in the phase difference between a pulse
and a previously transmitted pulse. The previously transmitted pulse may
be the immediately preceding pulse in the same frequency band, or may be
separated from the present pulse by a number of intervening pulses.